Video cameras find use in industrial control systems where they are used for inspection of products and the monitoring of processes. Electrical signals from the video camera, typically employing a charge coupled device ("CCD") as the imaging element, are digitized and stored in a computer memory to be processed by image processing techniques well known in the art to provide control signals useful in controlling and monitoring the process.
The high data transfer rates required by image acquisition necessitates specialized image acquisition circuitry. This circuitry operates independently of the industrial processor to coordinate digitizing and storing the video data from the camera by providing various control and timing signals. Such control and timing signals may include vertical and horizontal drive signals ("VD" and "HD", respectively). As is understood in the art, the VD and HD signals are used to synchronize the acquisition of the lines of video data as they are transmitted between the camera and the acquisition circuitry. The acquisition circuitry may also provide signals to the associated video processing equipment indicating when the acquired data is valid and to a strobe light to synchronize the operation of a strobe light with the camera's acquisition of a given frame of data. Further, for cameras which can be reset, in order to begin acquisition immediately rather than at the start of a continuous scan, the acquisition circuitry may provide various control and timing signals to initialize the video camera prior to data transfer.
Desirably, the acquisition circuitry may work with a variety of different cameras from different manufacturers. Generally, such cameras require different timing and control signals occurring at different times in the acquisition of data. Specialized, high speed acquisition circuitry is typically limited in its operation to working with a limited set of video camera types. Simple, high speed operation is obtained at the cost of little programmability.
In order to provide greater flexibility in the generation of timing and control signals for different video cameras, it is known to use a large memory for the storage of such timing and control signals. During image acquisition, the data of the memory is read-out on a continuous basis. Bits are set in the memory to correspond to times when control and timing signals should be generated. Thus, by the proper programming of the memory (i.e., setting and resetting of selected memory bits), an arbitrary set of timing and control signals may be developed. Because the generation of the control and timing signals simply requires a reading of the memory, it is extremely fast, matching the speed requirements of modern video systems. Further, such an approach allows control signal transitions to occur at single pixel resolution.
One drawback to using a continuously scanned memory to create timing and control signals is that for cameras with high resolution and multiple timing and control signals, extremely large and costly memories are required. Changing the camera configuration, which may require rewriting the entire memory, is time consuming.